POLYDOBA. 197 



Alex. Agassiz (I860) 1 describes the young stages of a species which he identifies with 

 Polydora ciliata, Johnston, but there exists doubt as to its specific relationships. His 

 earliest stage shows short tentacles, twelve bristled segments, and three crotchets in the 

 fifth, and his latest is nearly adult in character. He also makes remarks about Leucodora, 

 Johnston, as if the genus could be separated from Polydora, Bosc. His figures generally 

 are excellent, though the minute structure of the distinctive bristles is not given with 

 such detail as to ensure accurate diagnosis. He found the adults in tubes amongst mud 

 between tide-marks, and mentions that the larvae are easily reared to the stage of tube- 

 formation. He specially alludes to the lateral glands in the posterior region (behind the 

 great crotchets of the fifth segment). 



Claparede (1868) took note of the glandular pouches which are highly developed in 

 segments seven to ten of Polydora Agassizii (a form closely allied to P. ciliata) ; and the 

 flask-shaped cells of which are so characteristic. He also describes the segmental organs 

 as folded ciliated tubes with an internal and external opening, and which in the sexual 

 region at maturity undergo considerable enlargement. 



Claparede and Mecznikow (1868) describe and figure a larva of Polydora of a pyri- 

 form outline and about a dozen bristled segments, the fifth having its special bristles. It 

 is a telotroch larva with a protrotroch in front, and the anterior region is speckled with 

 brownish pigment. 



Ray Lankester (1868) 2 thought that the boring of Polydora and other forms was due 

 to an acid, but while it is true that boring occurs very extensively in calcareous rocks, 

 yet it also occurs in sandstone and shale impermeable to an acid, and consequently this 

 theory was withdrawn shortly afterwards. 



Prof. Haswell 3 (1880) makes some noteworthy remarks on the perforation of 

 Australian oysters by a Polydora resembling P. ciliata, and gives a description of a new 

 species. 



Carazzi (1893) gave a careful historical account of the genus, instituting a new sub- 

 genus (Boccardia) for Has well's Polydora polybranchia — the branchiae in which begin on 

 the second setigerous segment, and the hooks of two kinds on the fifth — and besides 

 referring to the species of Polydora then known, added a variety (pmlclira) of P. antennata 

 Claparede. His second sub-genus is distinguished from the first (Boccardia) by the 

 branchiae commencing on the sixth setigerous segment, and by the hooks on the fifth 

 being of one kind. 



One of the most complete accounts of the genus and species is that of Mesnil (1896), 

 and he gives a tabular view of the characters by which each form can be recognised. If 

 anything, this able author makes, perhaps, too much of slight distinctions, and thus 

 inclines to increase the number of species. He also gives a comparative series of the 

 pygidia of the several species. He was of opinion that the large modified bristles of the 

 fifth segment perforate hard rocks. 



Benham 4 (1896) made a separate family for Polydora (Polydoridae) mainly on 

 account of the special armature of the fifth segment, but this is on the whole unnecessary. 



1 ' Ann. Lyceum Nat. Hist. N. York/ vol. viii, p. 323. 



2 ' Ann. Nat. Hist./ ser. 4, vol. i, p. 234. 



3 ' Jottings from the Biol. Laborat. of Sydney University/ p. 274. 



4 Op. cit., p. 323. 



